Multiple myeloma (MM) is an incurable malignancy that afflicts 15,000 new Americans each year. Patients typically die 3.5 years after diagnosis, experiencing bone destruction leading to spine deformities and pain. Despite its transformation, the malignant clone is often dependent on growth factors in its environment, not for growth - MM is a slowly proliferating disease - but for survival. The objective of this study is to critically test the hypotheses that neurotrophin signaling contributes to these survival signals, and that inhibition of neurotrophin signaling will control MM progression. Trk receptor tyrosine kinases and their neurotrophin ligands are expressed by MM cells, creating a signaling loop that promotes the survival of MM cell lines and primary MM cells in vitro. Blockade of Trk signaling, using a soluble Trk-Fc decoy receptor, inhibits MM growth in a xenograft model. Neurotrophins are also expressed by bone marrow stroma, by endothelial cells, by osteoblasts, and thus contribute to the support of MM within its favored environment. These observations suggest a neurotrophin-Trk axis in MM tumor progression, and led to preclinical evaluation of cep701 as anti-MM therapy. Cep701 is a derivative of the indolcarbazole, K252a, with an IC50 of 3 nM for Trk and for Jak2. It specifically kills both primary MM cells and MM cell lines in culture, and inhibits growth of MM cell lines implanted into the subcutaneous tissue of NOD-SCID mice. The ability to target both Trk and Jak2 likely underlies its potent anti-MM activity. This study will evaluate the role of Trk signaling in MM disease progression. Specifically, we will: 1) Determine the importance of neurotrophin: Trk signaling to MM tumor survival, by assessing cell viability after disrupting Trk activation alone and in combination with Jak2 inhibition. 2) Delineate the signaling cascades that are critical to the pro-survival effects of neurotrophin:Trk activation in MM. 3) Identify the prevalence of Trk and neurotrophin expression by MM, and correlate this expression with disease characteristics including stage, prior therapies, immunoglobulin isotype, and cytogenetics, 4) Establish whether dual Trk/Jak2 targeting using cep701 will control MM disease progression in the SCID-hu model of MM.